2009 vcaa 3d .. how did they work out Z value?

[matt123]

Hey guys
http://www.vcaa.vic.edu.au/vcaa/vce/studies/mathematics/cas/pastexams/2009/2009mmCAS2-w.pdf

Q3d
how do u work out the Z value?

[matt123]

?

[InitialDRulz]

we are asking the same in this thread posted an hour ago

http://vcenotes.com/forum/index.php/topic,33059.0.html

also!!! they used 99.5% but WHY!

[matt123]

we are asking the same in this thread posted an hour ago

http://vcenotes.com/forum/index.php/topic,33059.0.html

also!!! they used 99.5% but WHY!

Problem is
no one explained how to actually find the Z value
i got no clue.
someone please help

[stonecold]

0.5% need to be under the range, and 0.5% need to be over.

Therefore, to get a z-value, you just go invNorm(0.005,0,1)  Remember that 0.5% is 0.005.

then to get s.d. you just rearrange the z score formula

z=(x-mean)/s.d.

s.d.=(x-mean)/z

s.d.=(65.6-67)/-2.57583

     = 54mm

[davidle_10]

Well u know that 99% of balls from 65.6<X<68.4. So that means there are two areas outside this interval: (-∞, 65.6] and [68.4,∞). So the are in each of these is (1-.99)/2=0.05. Then you know the area from (-∞, 65.6] is 0.005. So the z value that corresponds to this is found by using invNorm(Area=0.005,µ=0, sd=1)

[matt123]

0.5% need to be under the range, and 0.5% need to be over.

Therefore, to get a z-value, you just go invNorm(0.005,0,1)  Remember that 0.5% is 0.005.

then to get s.d. you just rearrange the z score formula

z=(x-mean)s.d.

s.d.=(x-mean)/z

s.d.=(65.6-67)/-2.57583

     = 54mm

Buddy
it wont work for me
i go to INV norm

type
0.005 prob
1
0

and i get "invalid"

lol

[3Xamz]

http://vcenotes.com/forum/index.php/topic,33059.0.html

[Whatlol]

Just go to normal distrubution and then write in lower and uper terminals, and mean. then write x for S.D.

then make that expression = 0.99 and solve for x.

[matt123]

Just go to normal distrubution and then write in lower and uper terminals, and mean. then write x for STD.

then make that expression = 0.99 and solve for x.

yeah i did and it worked thanks

but where did u get 0.995 from? isnt it 0,997?

[matt123]

btw
did it again'
and it worked thanks

but where did u get 0.995 from? isnt it 0,997

[3Xamz]

.997 is for 3 standard deviations either side of the mean.
We want .99, so the whole .997 mumbo-jumbo is irrelevant

[matt123]

.997 is for 3 standard deviations either side of the mean.
We want .99, so the whole .997 mumbo-jumbo is irrelevant

so then how did u get .995?

[Whatlol]

.997 is for 3 standard deviations either side of the mean.
We want .99, so the whole .997 mumbo-jumbo is irrelevant

so then how did u get .995?

its because on either side of 0.99 is 0.005

[3Xamz]

LOL refer to the other thread we were talking in.